The present invention relates to cooling medium supply and return tubes for conveying cooling medium to and from the buckets of a gas turbine and particularly relates to retention sleeves for preventing unrestrained axial movement of the thermal medium supply and return tubes, e.g., due to thermal response.
In an advanced gas turbine design for industrial power generation, the rotating buckets on the turbine rotor are preferably cooled by supplying a thermal medium, for example, steam, to the buckets. The steam is supplied generally through an axial bore tube assembly and radial tubes to a plurality of circumferentially spaced supply tubes extending axially adjacent the rim of the rotor. The supply tubes extend through openings in the stacked wheel and spacer arrangement of the rotor and communicate with a supply manifold adjacent a forward portion of the rotor. The manifold, in turn, includes a plurality of cross-tubes for supplying the steam to the forwardmost wheel and buckets carried thereby. Cooling steam is also supplied from the supply manifold to the buckets of the second-stage wheel. Spent cooling steam flows from the buckets of the first-stage wheel to a return manifold. Spent cooling steam also flows from the buckets of the second-stage wheel via a plurality of cross-tubes to the return manifold. The spent cooling steam is conveyed from the return manifold to the aft end of the rotor by way of return tubes circumferentially spaced about the rotor rim. The return tubes lie in communication with radially extending tubes whereby the spent cooling medium is returned axially through the bore tube assembly to a steam source or for use in steam turbines in a combined-cycle system.
Supply and return cross-tubes have in the past been provided with self-locking threaded inserts to retain the tube against axial movement. However, such designs are not acceptable because they require machine threads in the spacer wheel and limit access to the removed threaded insert if it is damaged. The cross-tubes must, however, be restrained from axial movement, e.g., motion caused by thermal response. During turbine startup and shutdown, the cross-tubes can thermally bind and unbind, causing the tubes to move axially, e.g., due to such thermal ratcheting. This causes the steam seals to disengage with subsequent loss of cooling to the buckets. There has thus developed a need for a removable, easily maintained device which can withstand high operating temperatures and large accelerations, have high cycle fatigue endurance, will not buckle under loads caused by thermal ratcheting and does not adversely affect the design of the spacer wheel.
In accordance with a preferred embodiment of the present invention, there is provided a cross-tube retention sleeve for preventing axial movement of the thermal medium cross-tubes, e.g., due to thermal ratcheting and which does not adversely affect the performance of the spacer wheel. It will be appreciated that the cross-tubes extend through openings in the spacer and are cantilevered from axial end faces of the spacer. Spoolies interconnect the ends of the cross-tubes with additional passages in the wheels mounting the buckets. Spoolies comprise sleeves having spherical end portions for engaging within cylindrical ends of adjoining but spaced tubes. To prevent axial movement of the cross-tubes which might disengage or cause leakage in the spoolies, the present invention provides an axial retention sleeve for overlying the cantilevered end of each cross-tube between the spacer mounting the cross-tube and the end face of an adjoining wheel. Particularly, each cross-tube has a radial flange against which one end of a retention sleeve bears. The opposite end of the retention sleeve is spaced axially from the end face of the adjacent wheel, forming an axial gap accommodating limited axial movement of the retention sleeve. This limited axial movement accommodates movement, for example, resulting from thermal expansion of the cross-tubes but limits the movement to preclude binding of the tubes and disruption of the seals.
In a preferred embodiment according to the present invention, there is provided in a gas turbine rotor having stacked wheels and spacers and tubes for conveying a thermal medium between buckets of one of the wheels and a manifold, the tubes extending generally in an axial direction in openings through a spacer adjacent a rim of the rotor and having radially outwardly directed flanges, retention sleeves for limiting axial movement of the tubes in a first axial direction, each retention sleeve having a first end in opposition to an end face of a rotor wheel forming an axial gap therebetween and a second end butting the flange, whereby axial movement of the tubes closes the gaps to prevent further axial movement of the tubes in the first axial direction.
In a further preferred embodiment according to the present invention, there is provided in a gas turbine rotor having stacked wheels and spacers and first tubes for supplying cooling steam to buckets of a first rotor wheel and second tubes for returning spent cooling steam from the buckets of a second rotor wheel, the tubes extending in a generally axial direction in openings through a spacer between the first and second rotor wheels and adjacent a rim of the rotor, each of the tubes having radially outwardly directed flanges, first and second retention sleeves for preventing axial movement of the first and second tubes in respective first and second axial directions, the first retention sleeves having first ends in opposition to an end face of the first rotor wheel and forming axial gaps therewith, the second retention sleeves having first ends in opposition to an end face of the second rotor wheel and forming axial gaps therewith, each of the first and second sleeves having second ends butting respective flanges of the first and second tubes, whereby axial movement of the tubes responsive to thermal expansion thereof closes the gaps to prevent further axial movement of the first and second tubes in the first and second axial directions, respectively.